As the temperature of hot junction increases, the thermo emfa)Always increasesb)Always decreasesc)May increase or decreased)Always remains constantCorrect answer is option 'C'. Can you explain this answer?

Question

Answer

Answer

In a thermocouple when the hot junction temperature is raised, the galvanometer shows a deflection which is directly proportional to the thermoelectric current and hence the thermo e.m.f. When the temperature is further increased, there is a state reached when the thermo e.m.f is maximum.

This value called neutral temperature (θn). The given thermocouple has a neutral temperature that has a fixed value and does not depend on the colder junction.
After further increasing the temperature, it is found that at a particular temperature we would see the thermo e.m.f decreases finally reaching zero. The temperature of the hot junction where there is reversal in the direction of e.m.f is called the temperature of inversion (θ

Answer

Explanation:

Introduction:
The thermo emf, also known as the thermoelectric voltage or Seebeck voltage, is a phenomenon that occurs when there is a temperature difference between two junctions of dissimilar metals or semiconductor materials. This temperature difference creates an electric potential difference, resulting in the generation of an electric current.

Effect of Hot Junction Temperature:
The temperature of the hot junction refers to one of the junctions where the temperature is higher compared to the other junction. The thermo emf is dependent on the temperature difference between the two junctions. Therefore, as the temperature of the hot junction increases, the effect on the thermo emf can be described as follows:

1. May increase: The thermo emf generated may increase.
2. May decrease: The thermo emf generated may decrease.
3. May remain constant: The thermo emf generated may remain constant.

Reasoning:
The behavior of the thermo emf with respect to the increase in temperature at the hot junction depends on various factors, including the material properties, temperature range, and specific setup of the thermocouple or thermoelectric device. Here are some key factors that influence the behavior:

1. Thermoelectric materials: Different thermoelectric materials exhibit varying temperature-dependent properties. Some materials have a positive temperature coefficient of thermoelectric power (Seebeck coefficient), which means that as the temperature increases, the generated thermo emf also increases. On the other hand, some materials have a negative temperature coefficient, resulting in a decrease in thermo emf as the temperature rises. Therefore, the specific material used in the thermocouple or thermoelectric device determines the effect of temperature on the thermo emf.

2. Temperature range: The behavior of the thermo emf can differ in different temperature ranges. Some materials may exhibit a linear relationship between temperature and thermo emf within a specific range, while others may show non-linear behavior. Therefore, the temperature range at which the thermocouple or thermoelectric device operates plays a significant role in determining the effect of temperature on the thermo emf.

3. Thermocouple configuration: The configuration of the thermocouple or thermoelectric device, such as the number and arrangement of thermocouple junctions, can also affect the behavior of the thermo emf with temperature. Different configurations can lead to different responses to temperature changes.

Conclusion:
In summary, the effect of increasing hot junction temperature on the thermo emf cannot be determined without considering various factors such as the specific materials used, temperature range, and device configuration. The thermo emf may increase, decrease, or remain constant depending on these factors. Therefore, option 'C' - 'May increase or decrease' is the correct answer.

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